QUANTUM MONTE-CARLO SIMULATION OF THE DYNAMICS OF THE SPIN-BOSON MODEL

This paper presents the results of stationary-phase Monte Carlo simulations for the dynamics of the spin-boson problem. The problem of alternating weights ubiquitous in dynamical simulations has been solved using discretized path-integral simulations in conjunction with stationary-phase filtering techniques. Our computation covers the bulk of the parameter space, including non-zero bias and frequency-dependent dissipation. Besides a comparison with analytic predictions, we present some new results. For sub-Ohmic dissipation, the dynamics at low temperatures depends significantly on the initial preparation. In the Ohmic regime 1/2 < K < 1, where K is Kondo's dimensionless coupling strength, we find significant deviations from the predictions of the non-interacting blip approximation at long times and low temperatures.